Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens, and the like. Touch screens, in particular, are popular because of their ease and versatility of operation as well as their declining price. Touch screens can include a touch sensor panel, which can be a transparent panel with a touch-sensitive surface, and a display device such as a liquid crystal display (LCD), light emitting diode (LED) display or organic light emitting diode (OLED) display that can be positioned partially or fully behind the panel so that the touch-sensitive surface can cover at least a portion of the viewable area of the display device. Touch screens can allow a user to perform various functions by touching the touch sensor panel using a finger, stylus, or other touch object at a location often dictated by a user interface (UI) being displayed by the display device. In general, touch screens can recognize a touch and the position of the touch on the touch sensor panel. The computing system can interpret the touch in accordance with one or more display images appearing at the time of the touch. The touch screen can perform one or more actions based on the touch. In the case of some touch screens, a physical touch on the display may not be needed to detect a touch. For example, in some capacitive-type touch screens, fringing electrical fields used to detect touch can extend beyond the surface of the display, and an touch object approaching near the surface may be detected near the surface without actually touching the surface.
Capacitive touch sensor panels can be formed by a matrix of partially or fully transparent or non-transparent conductive plates (e.g., touch electrodes) made of materials such as Indium Tin Oxide (ITO). In some examples, the conductive plates can be formed from other materials including conductive polymers, metal mesh, graphene, nanowires (e.g., silver nanowires) or nanotubes (e.g., carbon nanotubes). In order to detect such changes, in some examples, the touch electrodes can be coupled to sense circuitry using routing traces. It is due in part to their substantial transparency that some capacitive touch sensor panels can be overlaid on a display to form a touch screen. Some touch screens can be formed by at least partially integrating touch sensing circuitry into a display pixel stackup (i.e., a stack of material layers forming the display pixels). In some examples, touch screens can further include one or more shielding electrodes for mitigating the capacitive coupling of electrical noise to one or more touch sensing components (e.g., touch electrodes or routing traces) of the touch screen. The shielding electrodes can be located on the same layer or on different layers from the touch electrodes and/or routing traces and can receive a same or different signal from the signal applied to the touch electrodes (e.g., by way of routing traces) to sense a touch.